Swift - Java Programming: Python Programming: Master Programming Guide: Learn In A Day Series (Python, Java, SQL, PHP, HTML, Ruby)

import java.io.*; public class MyFirstProgram { public static void main(String[] args) { //This is my first java program System.out.println( Hello World !); } } import java.io.*; - The keyword import is used for including java libraries called packages which contain pre-defined functions that can be used in the program. Public class MyFirstProgram - this is the class definition, the key word public indicates that this class is available to all and class denotes to be a class definition. MyFirstProgram This is the name of a class. Name of the class having the main() function should be the same as the source file name. The class definition is enclosed within the parenthesis {} Public static void main (String args[]) : This is the main part of the program.

Since main() is the driver function, it should always be public. Static : You need to keep in mind that main() method should always be static because it makes the program memory efficient. Void : This is the return type of the method. This means that the main() method will not return anything. Main : name of the method. The interpreter starts execution from the main() method only.

Running a program means instructing the JVM to load the .class file which was compiled from the source code and start executing from the main() method. The two uses of the main method can be summarized as:

1. To Test all the other methods of the program
2. To Start execution of the program.

String[] args : is the argument that is passed to the main method. This method always takes an array of strings as its input parameter, and the array name should always be args. Note that the data type starts with a upper case S, this is because Strings is a class in Java and all class names start with upper case. The definition of the method is enclosed within flower braces{}, in this case, the only thing that we want our program to do is print Hello World! Toprint a statement to standard output console , System.out.println() ;is used. Note that all statements must end with a semi-colon (;) You can also use System.out.print () to display output, the difference is that println introduces a new line at the end of each statement it prints.

The other statement within the main() method in our program is called a comment statement. These are not compiled, the purpose of these statements which are preceded by // are only to give the programmer more information about code. Java doesnt have the concept of global variables at all, the same is achieved using keywords such as fina;, static, public.